Proanthocyanidins, namely condensed tannins are ubiquitous and they are among the most abundant natural phenol derivatives. Proanthocyanidin are mixture of oligomers and polymers composed of flavan-3-ol repeating units linked through C4-C8, or C4-C6 bonds. The flavan 3-ol units may also be doubly linked to by an additional double bond between C2-O7(A-type). The dimensions of proanthocyanidins are defined by the polymerization degree (DP).
The most common flavan 3-ols-contained in proanthocyanidins are Afzalechin, Epiafzalechin, Catechin, Epicatechin, Gallocatechin, Epigallocatechin. The proanthocyanidins consisting exclusively of catechin and epicatechin are the so called procyanidins, whereas those containing afzalechin and epiafzalechin or gallocatechin and epigallocatechin are the propelargonidin and prodelphinidin. Procyanidin are the most abundant in nature.
The biological activities of proanthocyanidins that have been reported in literature include antitumour, antiinflammatory, antiageing, antioxidant, antiallergic, antibacterial especially of the urinary tract, promoting hair growth, etc (Bart Schwitters/Jack Masquelier “21st century Biophylaxis substance OPC, Fragrance Journal, 50-135 (1997); Tomoya Takajashi et al., Journal of investigative dermatology 112 (310.316 (1999).
Many methods are known for preparing extract enriched in proanthocyanidins from plants or fruits of various origin such as cranberry (Vaccinium macrocarpon), grape seeds, tea leaves, peanuts, pine bark etc.
Some of these processes encompass extraction steps carried out with aqueous alcoholic solvents in the presence of mineral acids like for example the process in CN1454896, or they encompass the use of supercritical solvents like CO2 as disclosed in CN174923, or they require the use of ultra filtration membrane or involve reverse osmosis filtration as in the process disclosed in JP63267774.
Other processes require a combination of multiple extractions steps, using several type of organic solvents either alone or combined with each other, associated by at least one step wherein a solution containing the extracts is absorbed on a macroreticular polymeric resin, the absorbed liquid is subsequently eluted, concentrated and atomised as disclosed in the processes described in U.S. Pat. No. 6,608,102, U.S. Pat. No. 6,440,471.
According to other processes it is possible to obtain extracts containing very high amounts of proanthocyanidins. For example it is possible to obtain extracts with total proanthocyanidins content ranging from 80-90% with oligomer proanthocyanidins (OPC) in amounts of from 23 to 45% with the process disclosed in CA2539724 involving the treatment of a plant like pine bark or an extract or juice thereof, with at least two type of a absorbents resins differing in at least one of the following characteristics, namely the type of material, pore radius, specific surface area and molecular weight distribution range or it is possible to obtain extracts having a total proanthocyanidins content of from 67 to 85% and an OPC content of from 12.5 to 51%, with the process disclosed in EP1602653 comprising subjecting an extract or a squeezed juice of a plant to a combination of a treatment with a salt or an alkaloid and a treatment with a synthetic absorbent. resin
Notwithstanding the plethora of prior art processes allowing to obtain extract having a high titre in proanthocyanidins, commercially available extracts have a proanthocyanidins titre not exceeding 7%.
This means therefore that the prior art processes for preparing extract having a high titre in proanthocyanidins are not easily realisable on an industrial scale, for many reasons such as for example the use of toxic extraction solvents or extreme extraction temperature (about 100° C.) for long period of times (about 24 hours), the use of under pressure devices like in the case of supercritical fluids, or the use of ultrafiltration membrane.
The need was therefore felt to have a process for preparing extracts having a high proanthocyanidins titre not suffering the drawback of the prior art processes and that therefore could be easily realisable on an industrial scale.